Microelectronics chips such as integrated circuits are made from comparatively large wafers of semiconductor material. This process typically involves multiple successive steps including the following: generation of an etch mask photolitographically; etching of a layer of material as defined by the mask; removal of the photolithographic mask through some combination of wet and dry chemical techniques; and deposition of layers of materials. The photolithographic mask is formed from a polymeric material called a photoresist. After the photoresist mask has been removed, a final cleaning step, called rinsing or wet cleaning, is typically performed.
Deionized (DI) water is known for its use in this rinsing of semiconductor devices. It is known to prevent any metal corrosion and contamination of the devices. In order to make the wet cleaning more effective, gases such as carbon dioxide (CO2) and nitrogen (N2) have often been mixed with the DI water. Rinsing with carbonated deionized (DI-CO2) water is an electrically inert process that allows for damage free cleaning while maintaining the device integrity.
Carbonated deionized (DI-CO2) water can be created by inserting carbon dioxide (CO2) and water (H2O) or deionized (DI) water into a contactor. The contactor allows for the carbon dioxide (CO2) and the water (H2O) to directly contact one another without dispersing one phase into the other. There exists various types of contactors. For example, membrane contactors allow for a “bubble free” carbonated deionized (DI-CO2) water but cause a low CO2 mass transfer efficiency due to diffusion rates of CO2 through the membrane located therein. In addition, the membrane of the membrane contactor has a limited lifetime and requires regular maintenance. Another example of a contactor is a packed column type contactor. Packed columns typically have a high mass transfer efficiency, however the packed column presents several disadvantages. For example, the high mass transfer efficiency requires that the packed column is filled mostly with CO2 while H2O rinses over a high surface area of the packed column's tower packing. Flowing CO2 gas through a continuous H2O phase is inefficient because the bulk of the H2O provides a high diffusion resistance compared to the thin water film rinsing down the tower packing. Thus the diffusion rate of the CO2 into the H2O is limited. Further, a continuous H20 phase can require extraneous and expensive measurement devices to control a level of H2O in the packed column because if the H2O level becomes too high, the CO2 gas flows mostly through the H2O resulting in a less efficient operation. Also, a continuous H20 phase can require controlling of the level of H2O to avoid CO2 in the H2O outlet and H2O in the CO2 outlet. Further disadvantages of the packed column are as follows: 1) CO2 is lost at the outlet of an inert gas that is typically used in the packed column, 2) the injection of the inert gas can lower the CO2 concentration, thus lowering the overall mass transfer efficiency.
Controlling the proportions of these gases require considerably complex instrumentation and high costs which are significant disadvantages of current methods. Typically, an excess of gas is used which can lead to toxicity and disposal problems with respect to the unused gases particularly carbon dioxide. As a result, these processes are expensive and cumbersome.